1. Field of the Invention
This invention relates generally to hemodialysis or artificial kidney systems for treatment of blood to remove waste impurities and undesirable components therefrom, and more specifically, to an improved hemodialysis system which overcomes cross-contamination problems associated with multiple patient use of the system.
2. Description of the Prior Art
Hemodialysis systems have been in general use for a number of years in the treatment of renal disease and disability, and have proven highly effective in providing artificial kidney functions for persons whose own natural kidneys are functionally impaired. In operation of the hemodialysis system, blood containing waste substances, such as for example urea, creatinine, excess electrolytic salts and water, is withdrawn from the body and flowed through a dialyzer in indirect mass transfer relationship with an aqueous dialysate solution. The dialyzer may be of various conventional types including a mass transfer member such as an extended surface elastomeric membrane or a hollow fiber bundle across which the waste substances are transferred by concentration gradient (solute impurities) or osmotic pressure (water) from the blood to the dialysate solution. From the dialyzer the blood which has thus been depleted in impurities is returned to the patient's body. The impurity-enriched dialysate solution from the dialyzer is either disposed of to waste or else is regenerated as by sorbent means to remove the waste impurities therefrom prior to being recirculated to the dialyzer for renewed mass transfer from the blood to the solution.
Although artificial kidney hemodialysis systems have demonstrated widespread acceptance and effectiveness in use, the majority of such systems which have been developed to date are costly, large in size and heavy in weight. Accordingly, these systems have heretofore been primarily employed in hospital renal treatment facilities and "satellite" dialysis centers. The geographically fixed locations of these hemodialysis facilities tends to significantly restrict the mobility of persons requiring dialysis treatment and involves inherent problems of accessibility and expense of travel for persons living in sparsely populated areas or otherwise at great distance from the treatment center. Due to the widespread character of renal disease and disability, the aforementioned problems affect substantial numbers of the population; at present, for example, maintenance hemodialysis is employed to preserve and protect the lives of approximately 24,000 persons in the United States alone. One of the greatest limitations of the dialytic regimen of treatment imposed on these patients is a forced alteration in life style as associated with the need for physical attachment to a hemodialysis system two or three times each week.
In an effort to ease the problems of geographical confinement of individual hemodialysis patients, patient travel in groups to areas served by dialysis centers within and outside of the United States has been organized by patient associations such as the National Association of Patients on Hemodialysis and Transplantation (NAPHT). Despite such efforts, however, medical and scheduling problems continue to impede free travel by the dialysis patient. For example, domestic dialysis centers may be filled to capacity and thus unable to accept guest patients. Foreign dialysis centers may be prohibitively expensive or absolutely closed to tourists or visiting patients.
Under the foregoing considerations, a particular problem is faced by patients who are hepatitus carriers, i.e., whose blood is Australian antigen positive, since they are generally excluded from all centers and thus are denied travel opportunities. Such exclusion results from the potential for cross-contamination of other patients from viral residues in the dialysate flow circuit of the hemodialysis system after use of the system by a hepatitus carrying patient. In conventional practice, the patient is joined to the dialyzer means in a closed flow loop by means of connecting lengths of flexible elastic tubing joined in turn to an arteriovenous shunt or fistula attached to the patient. Inasmuch as the dialyzer means, shunt and connective blood flow tubing are generally disposable or susceptible to sterilization for re-use without undue difficulty, the treatment of blood containing viral hepatitus by such equipment poses no particular difficulty. Nonetheless, during dialysis, such viral contaminants are able to diffusionally pass through the mass transfer surface, i.e., dialyzer membrane, from the infected blood to the dialysate solution flowed through the dialyzer.
The above described entry of contaminant species into the dialysate solution flow circuit during treatment results in a potential health hazard not associated with the blood flow circuit. This is because the dialysate solution flow circuit, unlike the blood flow circuit, is neither disposable in its entirety or readily adaptable to complete sterilization. Various physical characteristics of the dialysate solution in the dialysis system during treatment are extremely critical and, accordingly, a number of processing, monitoring, adjustment and control steps are typically employed in the dialysate solution flow circuit to insure effectiveness of the dialyzing operation and concomitant protection of the patient. For example, heating and temperature control means are generally utilized in the dialysate solution flow circuit to maintain the temperature of the dialysate solution therein at a proper level, e.g. 98.degree.-100.degree. F, to prevent undue heating or cooling of the blood by heat exchange with the dialysate solution and to prevent hemolysis. In addition, conductivity of the dialysate solution is characteristically monitored to insure that the solution has the proper level of salinity and electrolytic characteristics. Such provision is made so that vital components of the blood are not lost to the dialysate solution by ion diffusion across the mass transfer surfaces in the dialyzer. Finally blood leak detection means are generally coupled to the dialysate solution flow circuit to insure that only indirect mass transfer-i.e., diffusional and osmotic transfer of species across the dialyzer membrane-is occurring, without direct cross-leakage between the respective fluids in the dialyzer.
Due to the necessity of utilizing the above-mentioned monitoring and equipment means in the dialysate solution flow circuit, such flow circuits are not disposable in the manner of the previously-described blood flow circuits. Furthermore, such dialysate solution flow circuits are difficult to effectively sterilize due to the liklihood of damage to the sensitive monitoring and control components coupled into the circuit by chemical sterilizing agents or elevated temperature sterilizing techniques. Thus, the problems associated with potential cross-contamination in dialysis treatment due to multiple patient use of the hemodialysis system are substantial and have not been satisfactorily overcome by the prior art.
Accordingly, it is an object of the present invention to provide an improved hemodialysis system for the treatment of blood to remove waste impurities therefrom.
It is also an object of the invention to provide a hemodialysis system in which cross-contamination problems associated with multiple patient use of the system are readily overcome.
It is another object of the present invention to provide a hemodialysis system of the above type which is compact, lightweight and readily portable.
Other objects and advantages of the invention will be apparent from the ensuing disclosure and appended claims.